Japanese Patent Publication No. 16044/71 (corresponding to U.S. Pat. No. 3,511,178) teaches a dry PS plate, which comprises a silicone rubber layer provided through an adhesive layer on a light solubilizable diazo light-sensitive layer backed with an aluminum plate, and which is exposed to light through a negative film, and thereafter the solubilized light-sensitive layer is removed by dissolution with a developing solution simultaneously with removing the silicone rubber layer provided on said layer, by which the aluminum plate is exposed to form an image part.
Japanese Patent Application (OPI) Nos. 80046/81 (corresponding to U.S. Pat. No. 4,342,820), 110249/80 (corresponding to British Pat. No. 2,034,911) and 59466/80 (corresponding to U.S. Pat. No. 4,358,522), teach a negative working dry PS plate, which comprises a silicone rubber layer provided on a light-sensitive layer composed of an o-quinonediazide compound supported by a base, and which is exposed to light through a negative transparency, and then the silicone rubber layer of the exposed part and, if necessary, the light-sensitive layer of the exposed part are removed with a developing solution, by which the light-sensitive layer or, if necessary, the support is exposed to form an image part (the term "OPI" as used herein refers to a "published unexamined Japanese patent application").
However, in these negative working dry PS plate, since only the silicone rubber layer in the exposed part or both the silicone rubber layer and the light-sensitive layer are removed by development to form an image part, while the silicone rubber layer in the non-exposed part is allowed to remain after development to form a non-image part, by which a lithographic plate requiring no dampening solution is produced, the light-sensitive layer of the non-image part (namely, the non-exposed part) has light sensitivity after development processing. As a result, and it is exposed by sunlight or fluorescent lamps in the room. In addition, the printing plate has an opportunity to be contacted with organic solvents analogous to the solvent for development, for example, with a plate cleaner or a printing ink in the printing step. In such a case, if good image reproduction is attained in the development step, there is an essential fault that the silicone rubber layer of the non-image part comes off by corrosion with the organic solvents when the light-sensitive layer is subjected to re-exposure.
In order to solve such a problem, processes which comprise fixing a negative working dry PS plate by thermal treatment after it is exposed to light and developed (Japanese Patent Application (OPI) Nos. 60947/80 and 192956/82) have been proposed. However, processes described in these Japanese Patent Applications have disadvantages in that they require an apparatus for thermal treatment and it is still not possible to completely prevent the silicone rubber layer from coming off of the non-image part because fixation of the non-image part is insufficient under such a thermal treatment condition. Japanese Patent Application (OPI) No. 205740/82 discloses a process which comprises fixing by processing with base after exposure and development, but it is understood that sufficient fixation of the non-image part is not attained by such a process.
Further, Japanese Patent Application (OPI) No. 17552/84 discloses a negative working dry PS plate, which comprises a light-sensitive layer containing an o-quinonediazide compound and a carboxylic acid, and which is imagewise exposed and developed after processing with a base or processed with a developing solution containing a base, by which the development latitude expands and, at the same time, the non-image part is fixed. However, in this case, it is understood that satisfactory fixation cannot be sufficiently carried out.